Apr 7 2011 4:48 PM

Sleep Study

Sleep studies can help cardiologists diagnose:

Sleep-related breathing disorders (such as sleep apnea)
Sleep-related seizure disorders
Parasomnias (such as sleepwalking)
Narcolepsy
Insomnia
Circadian rhythm disorders.

Sleep studies allow doctors to measure how much and how well you sleep. They also help show whether you have sleep disorders and how severe they are.

Sleep studies are important because untreated sleep disorders can increase your risk for high blood pressure, heart attack, stroke, and other medical conditions. People usually aren't aware of their breathing and movements while sleeping. They may never think to talk to their doctors about sleep- and health-related issues that may be linked to sleep disorders.

Doctors can diagnose and treat sleep disorders. Talk to your doctor if you feel tired or very sleepy while at work or school most days of the week. You also may want to talk to your doctor if you often have trouble falling or staying asleep, or if you wake up too early and aren't able to get back to sleep. These are common signs of a sleep disorder.

Doctors can diagnose some sleep disorders by asking questions about your sleep schedule and habits and by getting information from sleep partners or parents. To diagnose other sleep disorders, doctors also use the results from sleep studies and other medical tests.

Types of Sleep Studies

Four common sleep studies are used to help diagnose sleep-related problems:

Polysomnogram, or PSG
Multiple sleep latency test, or MSLT
Maintenance of wakefulness test, or MWT
Actigraphy

Polysomnogram

A PSG is usually done while you stay overnight at a sleep center. A PSG records brain activity, eye movements, heart rate, and blood pressure.

It also records the amount of oxygen in your blood, how much air is moving through your nose while you breathe, and chest movements that show whether you're making an effort to breathe. In some cases, breathing sounds, including snoring, also are recorded.

PSG results are used to help diagnose:

Insomnia
Sleep-related breathing disorders (such as sleep apnea)
Narcolepsy (PSG and MSLT results will be reviewed together)
Sleep-related seizure disorders
Parasomnias (such as sleepwalking)

Your cardiologist also may use a PSG to find the right setting for you on a continuous positive airway pressure (CPAP) machine. CPAP is the most common treatment for sleep apnea.

A CPAP machine uses a small pump to gently supply air to your nose or mouth through a special mask. The right setting involves adding just enough extra air to create mild pressure that keeps your airways open while you sleep.

If your doctor thinks that you have sleep apnea, he or she may schedule a split-night sleep study. During the first half of the night, your sleep will be checked without a CPAP machine. This will show if you have sleep apnea and how severe it is.

If the PSG shows signs that you have sleep apnea, you will use a CPAP machine during the second half of the split-night study. A technician checks your breathing using the PSG and adjusts the flow of air through the CPAP mask to find the correct setting for you.

A PSG also helps doctors:

Adjust CPAP settings after weight loss or gain
Recheck your sleep if symptoms return despite treatment with CPAP
Find out how well surgery has worked to correct a sleep-related breathing problem.

Multiple Sleep Latency Test

This daytime sleep study measures how sleepy you are. It's typically done the day after a PSG. You relax in a quiet room for about 30 minutes while a technician checks your brain activity.

The MSLT records whether you fall asleep during the test and what types and stages of sleep you're having. Sleep has two basic types: rapid eye movement (REM) and non-REM. REM sleep and non-REM sleep occur in patterns throughout the night.

The types and stages of sleep can help your doctor diagnose sleep disorders such as narcolepsy, idiopathic hypersomnia, and circadian rhythm disorders.

The test is repeated three or four times throughout the day. This is because your ability to fall asleep also changes throughout the day.

Maintenance of Wakefulness Test

This daytime sleep study measures your ability to stay awake and alert. It's usually done the day after a PSG and takes most of the day.

Results may be used to show whether your inability to stay awake is a public or personal safety concern or to check your response to treatment.

Actigraphy

This sleep study is done while you go about your normal daily routine. It doesn't require an overnight stay at the sleep clinic.

The actigraph is a simple device that's usually worn like a wristwatch. The doctor may ask you to wear the device for several days—except when bathing or swimming.